The present invention relates to an electromagnetic fuel injection valve for internal combustion engines.
Hitherto, electromagnetic fuel injection valves driven by electric signals from an engine control unit have widely been used in internal combustion engines for motor vehicles. The conventional fuel injection valves have a construction in which an electromagnetic coil and a yoke accommodating the coil are arranged around a stationary core of a hollow cylindrical shape (center core) and a nozzle body is mounted to the lower portion of the yoke. The nozzle body has fitted therein a movable unit having a valve element. The movable unit is urged toward a valve seat by force of a return spring.
A conventional electromagnetic fuel injection valves, as described in, for instance, JP-A-10-339240 is known to have a construction in which a magnetic fuel connector section, a nonmagnetic intermediate pipe section and a nonmagnetic valve body section are formed in one united body by magnetizing a single pipe made from a composite magnetic material and demagnetizing only an intermediate portion of the pipe through induction heating or the like in order to reduce the number of parts and improve the assemblability. In this electromagnetic fuel injection valve, a cylindrical stationary iron core is press-fitted into the fuel connector section, and a movable core with a valve element is installed in the valve body section. Further, an electromagnetic coil is arranged around an intermediate outer circumferential portion of the pipe, with the yoke mounted on the outer side of the electromagnetic coil. When the electromagnetic coil is energized, a magnetic circuit is established through the yoke, fuel connector section, stationary core, movable core, valve body section and yoke to magnetically attract the movable core toward the stationary core. The nonmagnetic section is employed to prevent a possible short-circuit of magnetic flux between the fuel connector section and the valve body section.
In the construction as described in JP-A-10-339240 that has the nonmagnetic intermediate pipe portion at an intermediate part of the pipe, however, magnetic flux leakage cannot be prevented sufficiently, resulting in a reduced magnetic force for attracting the movable core and therefore deteriorated the responsiveness.
In recent years, also in gasoline engines, fuel injection valves that directly inject fuel into cylinders have been put into practical use. As the direct injection type fuel injection valve, a so-called long nozzle type injector has been proposed in which a nozzle body provided on a lower portion of a yoke is made slender and long. When the long nozzle injector is to be mounted on a cylinder head in which an intake valve, an intake manifold and other components are closely arranged near the injector, only the slender nozzle body that does not occupy a large space can be installed in the cylinder head, so that large-diameter body portions such as the yoke and a connector mold are disposed apart from other components and cylinder head to have no interference therewith. This injector thus has an advantage of high degree of freedom for installation. However, a nozzle driven by the movable core inherently becomes long due to the long length of the nozzle body, and the nozzle weight also increases, thereby posing a serious problem of a response delay due to a reduced magnetic force.
An object of the present invention is to provide an electromagnetic fuel injection valve with improved responsiveness.
(1) To achieve the above objective, the invention provides an electromagnetic fuel injection valve which comprises a movable unit having a valve element, an electromagnetic coil, and a magnetic circuit for magnetically attracting the movable unit toward a valve opening side by energizing the electromagnetic coil. The magnetic circuit is composed of a hollow, cylindrical stationary core which defines a fuel passage extending axially through an injection valve body, a hollow seal ring made of a nonmagnetic or a feeble magnetic material, a hollow nozzle housing, and a movable core constituting a part of the movable unit, wherein the stationary core and the nozzle housing are coupled through the seal ring.
With this construction, it is possible to reduce flux leakage and improve a magnetic force and the responsiveness.
(2) In the above (1), preferably the seal ring has a flange at a lower portion thereof, a lower portion of the stationary core is press-fitted into an upper portion of the seal ring and welded thereto for sealing fuel, and the flange of the seal ring is press-fitted into a socket portion formed at an upper end of the nozzle housing and is welded thereto for sealing fuel.
(3) In the above (2), preferably, an outer circumference of a lower end of the stationary core is formed with a rounded or a tapered portion serving as a curved guide surface for press-fitting into the seal ring, and has a hard coating formed from a lower end face of the stationary core to the rounded portion or tapered portion.
(4) In the above (2), preferably, a contact surface between the movable unit and the stationary core is provided near an upper end of the flange of the seal ring.
(5) In the above (1), preferably the seal ring has a lower end portion formed to gently increase in inner diameter toward a lower end thereof, and an inner diameter of the lower end portion of the seal ring is larger than an inner diameter of the nozzle housing.
(6) In the above (1), the movable core preferably has a thin-walled portion at a lower portion thereof.
(7) In the above (1), the movable unit preferably comprises the movable core, the valve element and a joint for connecting the movable core and the valve element, and the joint comprises an upper cylinder portion, a lower cylinder portion smaller in diameter than the upper cylinder portion, and a tapered or spherical junction portion with a small fluid resistance for connecting the upper cylinder portion and the lower cylinder portion.
(8) In the above (7), the junction portion of the joint preferably has resiliency.
(9) In the above (8), a leaf spring is preferably provided between the movable core and the joint.
(10) In the above (7), preferably the junction portion of the joint has a hole for passage of fuel, and a total cross-sectional area of this hole is larger than a cross-sectional area of an axial fuel passage hole formed in the movable unit.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.